A gas circuit breaker enables a break by utilizing the superior insulation performance and break performance of an SF6 gas, but as the SF6 gas has a high global warming potential, a circuit breaker with a low environmental burden is demanded. Meanwhile, a vacuum circuit breaker enables a large current break owing to the superior insulation performance and break performance in a high vacuum. Also, as the vacuum circuit breaker does not use the SF6 gas and has a low environmental burden, the application of the vacuum circuit breaker to a high voltage is progressing.
Herein, in the case of the gas circuit breaker, a gas pressure is monitored by a manometer, and when the gas pressure falls below a gas pressure necessary for the insulation and break due to a gas leak, an anomaly signal is emitted, and the operation of the gas circuit breaker is locked. Meanwhile, in the case of the vacuum circuit breaker too, as the insulation and break performance cannot be maintained when a vacuum deterioration occurs due to a crack in a vacuum vessel, or the like, the method of monitoring the degree of vacuum is required.
As one technique of monitoring the degree of vacuum of the vacuum circuit breaker in a non-contact way, there is a method whereby an electromagnetic wave of a partial discharge occurring in the vacuum vessel when a vacuum deterioration occurs is detected by an antenna. The technique itself of detecting the electromagnetic wave of the partial discharge with the antenna is also commonly used in a gas insulated switchgear using an SF6 gas, and in the gas insulated switchgear, a high frequency component of a discharge of on the order of 500 MHz to 1500 MHz is detected. Meanwhile, it is known that the frequency of a partial discharge in a low vacuum is low compared with the heretofore described. In PTL 1, a vacuum deterioration is determined by detecting a signal component of 20 to 100 MHz of a discharge electromagnetic wave in a low vacuum when there is a vacuum deterioration.